This invention relates to formation of images on printing media, and, more particularly, to the operation of ink jet printers.
Printers are devices that print images onto a printing medium such as a sheet of paper. Printers of many types are available, and are commonly linked to a computer that defines and supplies the images, in the form of text or figures, that are to be printed. Some printers use a colorant-containing liquid, which may be an ink or a dye, but is often generically termed an ink in the industry, to form the characters on the printing medium. (By contrast, other printers use a dry toner to form the image.) Such printers deliver the colorant to the medium using a print head that creates the proper patterning of colorant to record the image.
One important type of printer is the ink jet printer, which forms small droplets of colorant that are ejected toward the printing medium in the pattern that forms the images. Ink jet printers are fast, producing a high output of print, and quiet, because there is no mechanical impact during formation of the image other than the droplets depositing upon the printing medium. Typically, an ink jet printer has a large number of individual colorant-ejection nozzles in a print head, oriented in a facing, but spaced-apart, relationship to the printing medium. The print head traverses past the surface of the medium, with the nozzles ejecting droplets of colorant under command at the proper times. The droplets strike the medium and then dry to form "dots" that, when viewed together, create the permanently printed image.
Good print quality is one of the most important considerations and bases of competition in the ink jet printer industry. Since the image is formed of thousands of individual dots, the quality of the image is ultimately dependent upon the quality and accurate placement of each dot, and the mode of arranging the dots on the medium. Because of the fashion in which the printing occurs, the quality of the dots can have a surprisingly large effect upon the final image quality, both for black-and-white and color images. The present invention is directed toward improvement of the image by improvements in the quality and placement of the printed dots.
From the practical standpoint of providing a printer that has a long, trouble-free life, the improvement of image quality has two aspects. One is attaining good image quality when using a new print head, and the other relates to maintaining image quality over extended use of the print head. Even though it may be possible to obtain good image quality with the initial use of the print head, the droplet size and/or placement accuracy may degrade with use due to mechanical, electrical, or hydraulic problems that develop, resulting in a degradation in image quality. Both considerations are important in designing print heads and nozzle structures.
Thus, there is a continuing need for improved ink jet printers wherein the dots forming the images are properly placed and of uniform size, and wherein the method of formation of the dots is resistant to degradation with extended use of the print head. The present invention fulfills this need, and further provides related advantages.